1. Field of the Invention
The present invention relates generally to marking scribes that encode data onto hard materials and more particularly to marking scribes that encode data represented by two-dimensional matrices.
2. Background Art
Marking systems used in applications such as part identification, tracking, inventory control, and order fulfillment are well known in the art. Early systems used characters attached to parts with tags, imprinted on parts with ink or paint, or punched into part surfaces. These forms of marking often required manual effort when marks were applied and additional manual effort when the marks were read. Later innovations including magnetic and optical alphanumeric data character recognition systems provided a degree of automated identification. A familiar and more recent system uses bar code recognition.
The previous and present systems solved many part identification problems and provided improved efficiencies, however a number of problems remain. For example, surface roughness and data character deterioration, debilitation and obscuration still affect identification accuracy and speed. Such problems usually worsen with time and wear, and demands for part tracking capabilities that extend beyond the manufacturing, storing and shipping of parts to the end of their useful lives have motivated the development of a two-dimensional marking process. This process features an advantageous pairing of small size and large data encoding capacity, and it facilitates full-life-cycle traceability of individual parts and assemblies.
The two-dimensional process, known as Direct Part Mark Identification (DPMI), includes the formation of a two-dimensional data matrix typically represented by a rectangular field of data cells arranged in columns and rows. The condition of each data cell represents a binary unit of information, and a number of processes have been developed to provide a detectable contrast between “marked” and “unmarked” data cells. Marking includes such processes as ink-jet printing, during which ink droplets are propelled onto the surface of a material being marked. Colored dye is left upon the surface when the ink evaporates. This process is capable of marking fast-moving parts and provides good contrast. Surfaces to be marked in this manner, however, often require preparation to ensure that the chemical reaction between the ink and the surface will maximize contrast and permanence of the mark.
Electrochemical etching is also used to mark part surfaces. During this process, a stencil is sandwiched between the part surface and an electrolyte-soaked pad; and a low electrical potential is applied across the part and the pad. This results in an oxidation of the exposed part surface, and produces a mark defined by the configuration of the stencil. This marking process commonly finds application in marking round surfaces and stress-sensitive parts. Disadvantages of electrochemical marking systems are that its automation can be difficult and that only conductive material can be processed.
Another part-marking process uses a laser to melt or vaporize the surface of a part to produce a detectable mark. Such a process can produce consistent, precision, round, square and linear marks at high speed. It is easily automated, requires no tool replacement, and requires only position fixturing. Marks produced are of high quality, but the quality is subject to interactions of the laser with the material being marked. Disadvantages of laser marking systems are that the equipment is relatively expensive and that the process is not readily applicable to irregular surfaces.
Dot peening is yet another part-marking process. It involves driving a stylus into the surface of a material being marked to leave, in a specific data cell, an indentation that contrasts with the surface of the material. The dot-peening process is relatively inexpensive, it produces good-quality marks, there is less material stress as compared to steel stamping processes, and there are no consumables. The parts, however, must be securely fixtured; and the noise level attending the process is relatively high. Also, in certain situations, marking surface preparation, such as cleaning or even machining, might be required to ensure code readability.